The present invention relates to a method of automatically isolating a faulty section of a power line belonging to an electrical energy supply network and also pertains to an arrangement for carrying out the aforesaid method.
It is known that power lines of high-voltage energy supply networks can be provided with automatic safety devices. Safety devices of this kind are used in particular for rapidly isolating faulty power line sections and for reconnecting them quickly after the fault has been eliminated. Safety devices of this kind prevent high-voltage energy supply networks from becoming damaged in the event of short circuits. Additionally they have the advantage of avoiding unnecessarily long breaks in operation in the event of temporary short circuits of the kind frequently encountered in practice. Safety devices of this kind are expensive, with the result that, as a rule, they only can be used economically in power lines serving large energy-supply areas. Accordingly, they are generally used only in high-voltage power supply systems of from about 50 kV upwards.
In contrast to such high-voltages power supply systems the isolation of faulty sections of a power line in so-called medium-voltage power supply systems of the kind operated, for example, at voltages of around 5 kV to 50 kV for supplying electricity to individual urban areas, is still generally carried out by hand at the section where the fault has occurred. The result of this is that, in the event of a fault, the isolation of the faulty section required for eliminating the fault takes a considerable amount of time, partly because the fault first of all has to be located and partly because, in towns, urban traffic conditions often make it difficult to reach the faulty section of the power line quickly once the fault has been located, while in country or rural areas access to the power lines is often difficult. As a result, numerous consumers served by the same power line are inconvenienced unnecessarily by the fault for a long period before it is corrected.
In order to avoid these difficulties, it is possible for example to provide a power line with circuit breakers for dividing it up into individual sections, these circuit breakers being provided with an automatic cutout. By suitably staggering the response time of the individual circuit breakers, it is possible, in a certain mains configuration, for only the faulty section to be automatically switched-off in the event of a fault.
Unfortunately, the automatic circuit breakers required are quite expensive and the staggering of the response times is governed by the mains configuration, with the result that, in the event of a change in the mains configuration, this system has to be adapted to the new conditions, i.e., the stagger may have to be changed.
Although arrangements are known which employ mostly isolators and only a few circuit breakers, for dividing up the power line into individual sections, these arrangements necessitate the use of signal-transmission systems and transmission channels that are independent from the aforementioned power line for eliminating a faulty section from the power line.
Arrangements have been developed for special cases, in which the power line only can be divided up into sections by circuit breakers, the individual circuit breakers being associated with transmission systems linked with one another through transmission channels independent of the power line.
In all solutions where isolators or on-load switches are provided for dividing up the power line, final elimination of the faulty section involves temporary isolation of the power line from its associated energy source, because switches of the kind referred to above are known to be unsuitable for isolating excess currents.
It would be desirable for economic reasons to use only inexpensive isolators for dividing up the power line into individual sections, and to use the considerably more expensive circuit breakers solely for connecting and disconnecting the power line as a whole to and from one or more energy sources. However, brief interruption of the flow of current to all the consumers connected to one and the same power line is in this case inevitable. This is economically preferable to having to keep all the consumers connected to the faulty power line waiting until the fault has been eliminated.
Other known arrangements are based on the so-called successive closing test, in which, in the event of a fault in a section of a power line, the power line affected by the fault is first divided up into its individual sections, after which the individual sections are successively placed under voltage again starting from the source. It is only in the event of switching on to a section which is still faulty that the power line is divided up again and the normally operating sections reconnected. Although these solutions are suitable for all standard mains configurations, they are confined to energy supply networks whose section switches are capable of switching on to a faulty section. Accordingly, it is necessary in this case to provide either circuit breakers or specially dimensioned on-load switches for separation into the individual sections. In other words, the inexpensive isolators cannot be used in this case, with the result that this arrangement is excessively expensive.
Arrangements which use signal transmission channels, for example in the form of control lines laid between the individual switches of the power line, have the disadvantages that such transmission channels are expensive and, because they are normally positioned near the power line, they are likely to be affected by faults in the power line, for example short circuits. This applies in particular as regards communications channels situated adjacent the power line in question. In this connection, reference is made to the publication "IEE Conference Publication No. 99 Part I: Contributions der Konferenz CIRED, London 1973", page 187, Section 3.2.2, to the use of the power line itself for signal transmission. However, it must be pointed out that, in the event of a fault, a signal has to be transmitted over a faulty section, which naturally jeopardises reliable signal transmission.